1. Field of the Invention
The field of the invention is that of digital data transmission. To be more precise, the invention concerns the switching of ATM (Asynchronous Transfer Mode) cells between a plurality of incoming channels and a plurality of outgoing channels.
2. Description of the Prior Art
The general principle of ATM transfer is well known and many switching techniques and architectures have been described. Conventionally, an ATM switching node comprises:
an input stage comprising a plurality of input terminal functions each receiving call data (cells) on a plurality of incoming channels, PA1 one or more switching stages formed of switching matrices, and PA1 an output stage comprising a plurality of output terminal functions each distributing cells to a plurality of outgoing channels, PA1 the whole being organized so that any cell received on any incoming channel can be directed to any outgoing channel. PA1 the various "ATC & QoS" traffics are separated and switched in different planes, PA1 the various "ATC & QoS" traffics are separated and switched in different buffers in each switching stage, or PA1 internal protocols are used between internal switching points, based on different algorithms and parameters. PA1 wherein each of said input terminal functions and said output terminal functions comprises, for each of said groups of connections, spacing means for re-establishing the nominal period of the cells of each of said connections or establishing a global period for all of the group. PA1 in each of said input terminal functions: PA1 in each of said output terminal functions processing received cells of a group of connections to associate with each cell information necessary for its further routing, PA1 and further consists in, for each of said connection groups, spacing the cells to re-establish the nominal period of the cells of each of said connections or establishing a global period for all of the group.
Switching, i.e. transfer or routing of cells to the required outgoing channel, is usually controlled on a "by connection" basis. In other terms, a transfer path in the switching stages is defined and marked for each connection. A marker at each connection point indicates the path to be taken by each cell identified by its connection data.
This connection data is conventionally the virtual path (VP) and/or the virtual circuit (VC). Other routing information can equally be used for ATM connections internal to the switching devices.
Marking control utilizes relatively complex operations on each new connection and each disconnection. A new connection presupposes a search for an available path to the required outgoing channel and then marking each intersection of the identified path with information (VP/VC) enabling the source and the destination of each cell to be recognized. It also presupposes the presence of high-capacity memory means at each intersection for associating the routing data with each connection. Also, current standards distinguish a plurality of ATM transfer capabilities (ATC) and a plurality of qualities of service (QoS). In their "traffic contract" users can choose the "ATC" and the "QoS" they want.
At present day switching nodes this variety leads to the use of dedicated means. To be more precise:
Clearly these various solutions are complex in terms of both hardware and software. They are therefore costly in terms of processing time, memory capacity, etc.
Document U.S. Pat. No. 5,309,430 describes an ATM cell switching device comprising switching means interconnecting a plurality of input terminal functions with a plurality of output terminal functions and comprising means for creating groups of connections; all the connections of one group of connections coming from the same input terminal function and going to at least one common output terminal function, each of the cells of the connections of one group of connections being allocated the same connection group identifier for routing cells in said switching means.
This ATM switching process limits the number of operations to be effected when setting up a connection, in particular with regard to marking the path inside the switching network. It reduces the amount of memory required, in particular in the switching stages. Groups of connections (GoC) are defined so that a plurality of separate connections are treated in the same way in the switching means when they must be directed to the same output terminal function or functions. In this way marking in the switching stages is greatly simplified and established once and for all when the "GoC" is established.
The objective of the invention is to propose a process and a device optimizing cell delivery speed and timing approximating the nominal period of the cells.
Another objective of the invention is to simplify the specific processing operations imposed by the various "ATC" and "QoS".